1. Field of the Invention
The present invention relates to a gas sensor system which includes a gas sensor having an oxygen pump cell and an oxygen concentration detection cell, and a sensor control section for controlling the gas sensor.
2. Description of the Related Art
Conventionally, gas sensors such as a full-range air-fuel-ratio sensor have been known having two cells (an oxygen pump cell and an oxygen concentration detection cell) and an NOx sensor having three cells (the above-described two cells and a cell for detecting the concentration of NOx gas). Such a gas sensor constitutes a gas sensor system in cooperation with a sensor control section for controlling the gas sensor, and the gas sensor system is mounted on a vehicle or the like.
Some such gas sensors have three terminals electrically communicating with the oxygen pump cell and the oxygen concentration detection cell. Specifically, of the three terminals, first and second terminals communicate with a pair of electrodes of the oxygen pump cell. The second terminal communicates with one of a pair of electrodes of the oxygen concentration detection cell as well, and a third terminal communicates with the other electrode of the oxygen concentration detection cell. The sensor control section controls the gas sensor through these terminals.
Incidentally, in such a gas sensor system, a short anomaly may arises in which any one of the terminals of the gas sensor connected to the sensor control section may be shorted to a ground potential or a power supply potential, for example, the battery potential of a vehicle. Specifically, this may be a terminal itself or a wiring line which connects the terminal to short the cell to the ground potential or the power supply potential. Hereinafter, this state will also be expressed as “a terminal is shorted” or “short of a terminal”. If electric current is supplied to the gas sensor in a state in which such a short anomaly continues, an excessively large abnormal current flows to the oxygen pump cell and/or the oxygen concentration detection cell, and the gas sensor may deteriorate or fail. Therefore, conventionally, a method of diagnosing short anomalies in a gas sensor system has been proposed.
For example, Patent Document 1 discloses an anomaly diagnosing method of supplying a current for anomaly diagnosis to each cell of a gas sensor through connection points (corresponding to the above-described terminals), and determining, based on the potential of each connection point detected when the current is supplied, a location where a short anomaly has occurred, and the source (end) of the short-circuit (short to the ground potential or short to the power supply potential).
[Patent Document 1] Japanese Patent Application Laid-Open (kokai) No. 2006-47278